When pesticide solutions are sprayed by ground spray equipment or aircraft, droplets are produced by the nozzles of the equipment. Many of these droplets can be so small that they stay suspended in air and are carried by air currents until they contact a surface or drop to the ground. A number of factors influence drift, including the physio-chemical properties of the spray mixture, weather conditions, topography, the crop or area being sprayed, application equipment and methods, and decisions by the applicator.
Off-target spray can affect human health and the environment. For example, spray drift can result in pesticide exposures to farm workers, children playing outside, and wildlife and its habitat. Drift can also contaminate a home garden or another farmer's crops, causing illegal pesticide residues and/or plant damage. The proximity of individuals and sensitive sites to the pesticide application, the amounts of pesticide drift, and toxicity of the pesticide are important factors in determining the potential impacts from drift.
The EPA defines pesticide spray drift as the physical movement of a pesticide through air at the time of application or soon thereafter, to any site other than that intended for application (often referred to as off target). EPA does not include in its definition the movement of pesticides to off-target sites caused by erosion, migration, volatility, or contaminated soil particles that are windblown after application, unless specifically addressed on a pesticide product label with respect to drift-control requirements.
Each year there are thousands of reported complaints of off-target spray drift. Reports of exposures of people, plants, and animals to pesticides due to off-target drift (often referred to as “drift incidents”) are an important component in the scientific evaluation and regulation of the uses of pesticides. Other routes of pesticide exposure include consuming foods and drinking water which may contain pesticide residues, applying pesticides, and contacting treated surfaces in agricultural, industrial, or residential settings. The EPA considers all of these routes of exposure in regulating the use of pesticides.
In the past, conventional polymers of guar gum, acrylamide and other ethylenically unsaturated monomers have been used as anti-drift agents. It has been generally accepted that polymers which give optimum spray drift control are either non-ionic (eg acrylamide homopolymer) or have relatively low anionic content (e.g. 5 to 30 wt. %) and also have relatively high intrinsic viscosity, for instance above 6 dl/g. Such polymers tend to form viscous aqueous solutions unless used at low concentration. Normal practice is to mix the polymer powder or reverse phase emulsion form with water directly into the spray tank so as to form an aqueous solution of polymer. However, emulsion polymers can be difficult to activate in this situation and polymer powders take a long time to dissolve leading to many large, undissolved particles, resulting in a formulation exhibiting a high viscosity even at a very low polymer concentration. It is therefore sometimes necessary to use more polymer as a result of inefficient dissolution of the polymer in solution, typically on the order of at least 0.05 wt. %. Polymers of intrinsic viscosity in the range 6 to 15 dl/g are also typically utilized in the final spray solution. In addition to the above-problems, such aqueous liquid systems are not shear stable and irreversibly lose their utility due to the fact that high molecular weight polymers undergo mechanical degradation of their molecular weight.
Accordingly, there is a need to reduce the amount of drift exhibited by aqueous liquids which are used in agro applications using non-polymeric drift control agents.